A wide range of medical treatments have been previously developed using “endoluminal prostheses,” which terms are herein intended to mean medical devices which are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring or artificially made lumens. Examples of lumens in which endoluminal prostheses may be implanted include, without limitation: arteries such as those located within coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes. Various types of endoluminal prostheses have also been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted luminal wall.
A number of vascular devices have been developed for replacing, supplementing or excluding portions of blood vessels. These vascular grafts may include but are not limited to endoluminal vascular prostheses and stent grafts, for example, aneurysm exclusion devices such as abdominal aortic aneurysm (“AAA”) devices that are used to exclude aneurysms and provide a prosthetic lumen for the flow of blood.
One very significant use for endoluminal or vascular prostheses is in treating aneurysms. Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease or a genetic predisposition which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aneurysms occurring in the abdominal aorta. Typically an abdominal aneurysm will begin below the renal arteries and may extend into one or both of the iliac arteries.
Aneurysms, especially abdominal aortic aneurysms, have been most commonly treated in open surgery procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique in view of the alternative of a fatal ruptured abdominal aortic aneurysm, the open surgical technique suffers from a number of disadvantages. The surgical procedure is complex and requires long hospital stays due to serious complications and long recovery times and has high mortality rates. In order to reduce the mortality rates, complications and duration of hospital stays, less invasive devices and techniques have been developed. The improved devices include tubular prostheses that provide a lumen or lumens for blood flow while excluding blood flow to the aneurysm site. They are introduced into the blood vessel using a catheter in a less or minimally invasive technique. Although frequently referred to as stent-grafts, these devices differ from covered stents in that they are not used to mechanically prop open natural blood vessels. Rather, they are used to secure an artificial lumen in a sealing engagement with the vessel wall without further opening the natural blood vessel that is already abnormally dilated.
Typically these endoluminal prostheses or stent grafts are constructed of graft materials such as woven polymer materials (e.g., Dacron,) or polytetrafluoroethylene (“PTFE”) and a support structure. The stent-grafts typically have graft material secured onto the inner diameter or outer diameter of a support structure that supports the graft material and/or holds it in place against a luminal wall. The prostheses are typically secured to a vessel wall above and below the aneurysm site with at least one attached expandable annular spring member that provides sufficient radial force so that the prosthesis engages the inner lumen wall of the body lumen to seal the prosthetic lumen from the aneurysm. In some devices, a radially expandable member partially extends proximally in an axial direction from the graft material. The ring member is substantially uncovered, i.e., has openings through which blood may flow and is therefore useful in placing the device at or near the junction of other vasculature, e.g., at or near the renal artery where a stent graft is being used to exclude an abdominal aortic aneurysm. When the expandable member must be placed near the renal artery, for example, such an axially extending ring member may be used so that blood may flow through openings in the expandable member so that the renal arteries are not occluded. In other devices, other mechanisms have also been used to engage the vessel walls such as, for example, forcibly expandable members or hook like members that puncture the vessel wall. In some devices where attached expandable ring members are used, a support bar attaches the ring members to provide columnar support along the length of the bar.
One of the characteristics desired to prevent collapse of the stent graft is columnar strength. However, the features that provide columnar strength may also reduce device flexibility that permits sealing placement of the device within a tortuous vessel, such as, e.g., a diseased iliac vessel. Further, the devices are subject to cyclical loading and other stresses. Accordingly it would be desirable to provide a device structure having desired loading characteristics, with sufficient columnar strength, while maintaining sufficient flexibility to allow placement and sealing of the prosthesis within a tortuous vessel.
Additionally, to provide catheter access to the site and make it maneuverable through the tortuous or narrowed diseased vessels, it is desirable to provide a stent graft with a high degree of radial compressibility. Therefore, it is desirable to provide an endoluminal tubular graft that has sufficient strength and loading characteristics while maintaining flexibility and radial compressibility into for delivery from a relatively small diameter delivery catheter.
Further, it is important for the aneurysm exclusion device to sufficiently seal against the vessel wall to prevent blood from entering the aneurysm site as it flows through the artificial lumen. Accordingly, it would be desirable to provide an improved seal, especially at the proximal end of the prosthesis.